1. Field of the Invention
This invention relates to phase shifting circuits.
More especially, but not exclusively, the invention relates to phase shifting circuits suitable for use in alternating current (AC) electric power measuring systems to provide the 90.degree. phase shift on voltage or current input required to enable an active power measuring device to measure reactive power.
2. Description of Related Art
Conventionally such systems use for this purpose a phase shifting circuit comprising a passive, i.e. resistance-capacitance, network and a single operational amplifier. Such phase shifting circuits exhibit variation of phase shift and gain with frequency to an extent such that Ac power measuring systems incorporating them have a lower grade specification when measuring reactive power than when measuring active power.